Can you explain what it does? It looks like it is calling commands from different /usr directories...

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#!/bin/bash makes that the commands in the script are executed by the /bin/bash shell (otherwise the system doesn't know what to do with the commands).
And PATH sets the directories where the script searches for commands that don't have the full path in the script. For example, if the full path for the find tool is /usr/bin/find, and you only specify find in the script, the script doesn't find find if you don't specify /usr/bin in the PATH variable.
If you use /usr/bin/find instead of just find in the script, then you don't need a PATH variable.